Field of the Invention
The present disclosure relates to a cartridge used in electrophotographic image forming apparatuses and to an image forming apparatus.
Description of the Related Art
In general, image forming apparatuses include a photosensitive drum, an intermediate transfer belt (intermediate transfer member), and other members. Image forming apparatuses further include a cleaning blade to remove toner (residual toner) remaining on the photosensitive drum or the intermediate transfer member after transfer. The residual toner is collected from the photosensitive drum or the intermediate transfer member into a tonner collection container by bringing the free end of the cleaning blade into contact with the photosensitive drum or the intermediate transfer belt.
In order to increase toner collection performance, the region (cleaning nip) at which the cleaning blade and the photosensitive drum or the intermediate transfer member come into contact with each other is kept at a predetermined pressure (contact pressure) or more. On the other hand, a low torque is desirable at the contact region in view of the lifetime of the photosensitive drum or the intermediate transfer belt.
From the viewpoint of reducing the torque at the contact region, Japanese Patent Laid-Open No. 2015-22078 discloses a concept using a developer containing a toner and silica particles added. as an external additive, and in which a lubricant is applied onto the surface of the photosensitive drum.
Also, Japanese Patent Laid-Open No. 2003-280255 discloses a concept using a developer containing a toner containing an external additive, in which at least 1% of the external additive is separated from the toner particles and delivered as a lubricant to the contact region (nip portion), thereby reducing the torque at the contact region.
In both cases disclosed in the above-cited documents, the particles of the external additive present in the contact region (cleaning nip) function as very small rollers to reduce the torque. Unfortunately, the external additive gradually migrates downstream in the rotational direction of the photosensitive drum from the cleaning nip with the passage of time and contaminates the charging member located downstream from the photosensitive drum. This may a cause of defects, such as inconsistencies in density, in the resulting image.